Heart valves can be affected by several conditions. For example, mitral valves can be affected by mitral valve regurgitation, mitral valve prolapse and mitral valve stenosis. Mitral valve regurgitation is abnormal leaking of blood from the left ventricle into the left atrium caused by a disorder of the heart in which the leaflets of the mitral valve fail to coapt into apposition at peak contraction pressures. The mitral valve leaflets may not coapt sufficiently because heart diseases often cause dilation of the heart muscle, which in turn enlarges the native mitral valve annulus to the extent that the leaflets do not coapt during systole. Abnormal backflow can also occur when the papillary muscles are functionally compromised due to ischemia or other conditions. More specifically, as the left ventricle contracts during systole, the affected papillary muscles do not contract sufficiently to effect proper closure of the leaflets.
Mitral valve prolapse is a condition when the mitral leaflets bulge abnormally up in to the left atrium. This can cause irregular behavior of the mitral valve and lead to mitral valve regurgitation. The leaflets may prolapse and fail to coapt because the tendons connecting the papillary muscles to the inferior side of the mitral valve leaflets (chordae tendineae) may tear or stretch. Mitral valve stenosis is a narrowing of the mitral valve orifice that impedes filling of the left ventricle in diastole.
Mitral valve regurgitation is often treated using diuretics and/or vasodilators to reduce the amount of blood flowing back into the left atrium. Surgical approaches (open and intravascular) for either the repair or replacement of the valve have also been used to treat mitral valve regurgitation. For example, typical repair techniques involve cinching or resecting portions of the dilated annulus. Cinching, for example, includes implanting annular or peri-annular rings that are generally secured to the annulus or surrounding tissue. Other repair procedures suture or clip the valve leaflets into partial apposition with one another.
Alternatively, more invasive procedures replace the entire valve itself by implanting mechanical valves or biological tissue into the heart in place of the native mitral valve. These invasive procedures conventionally require large open thoracotomies and are thus very painful, have significant morbidity, and require long recovery periods. Moreover, with many repair and replacement procedures, the durability of the devices or improper sizing of annuloplasty rings or replacement valves may cause additional problems for the patient. Repair procedures also require a highly skilled cardiac surgeon because poorly or inaccurately placed sutures may affect the success of procedures.
Less invasive approaches to aortic valve replacement have been implemented in recent years. Examples of pre-assembled, percutaneous prosthetic valves include, e.g., the CoreValve Revalving® System from Medtronic/Corevalve Inc. (Irvine, Calif., USA) and the Edwards-Sapien® Valve from Edwards Lifesciences (Irvine, Calif., USA). Both valve systems include an expandable frame and a tri-leaflet bioprosthetic valve attached to the expandable frame. The aortic valve is substantially symmetric, circular, and has a muscular annulus. The expandable frames in aortic applications have a symmetric, circular shape at the aortic valve annulus to match the native anatomy, but also because tri-leaflet prosthetic valves require circular symmetry for proper coaptation of the prosthetic leaflets. Thus, aortic valve anatomy lends itself to an expandable frame housing a replacement valve since the aortic valve anatomy is substantially uniform, symmetric, and fairly muscular. Other heart valve anatomies, however, are not uniform, symmetric or sufficiently muscular, and thus transvascular aortic valve replacement devises may not be well suited for other types of heart valves.
The triscuspid valve on the right side of the heart, although it normally has three leaflets, poses similar challenges to less invasive treatment as the mitral valve. Therefore there is a need for a better prosthesis to treat tricuspid valve disease as well.
Given the difficulties associated with current procedures, there remains the need for simple, effective, and less invasive devices and methods for treating dysfunctional heart valves.